Whether
it be antioxidants, “natural sunscreen,” or modifications to metabolism such as
C4 and CAM processes, evolution has engendered many different mechanisms for
reducing free radical production and/or subsequent damage. The mechanism of
interest for this experiment is the natural sunscreen Blue Spruces have
invented and implemented – the blue powdery substance which coats many
Blue Spruce needles, distinguishing them from most other high altitude needle
trees and giving the spruce its name. By reflecting one of the highest energy
lights (blue), the Blue Spruce initially reduces light energy absorption, which
lessens the amount of energy available to create free radicals, especially when
the leaves’ stomata are closed during peak hours of sunlight intensity in which
the free radical prone oxygen is present in abundance and photosynthesis slows
due to diminished CO2concentration and subsequently increased bondage of O2 to Rubisco,
leaving extra energetic electrons (from the slowed rate of light dependent
reactions) to reduce oxygen, creating carcinogenic molecules dangerous to the
plant (free radicals). Although this innovation may help to protect the plant
from damage, my question is if there is a tradeoff – does the reduced
absorption of light energy affect the rate of photosynthesis?

Since
photosynthesis is dependent on the absorption of light energy, my hypothesis is
that decreased absorption of light energy due to the reflectance of blue wavelengths
will decrease the rate of photosynthesis. If this is true, blue coated Blue
spruce needles will have a slower rate of photosynthesis than non-blue coated
(i.e. green) Blue Spruce needles. We proceeded to test this hypothesis by
measuring and comparing the rates of photosynthesis between Blue Spruce sprigs
with green needles and those with blue coated needles. In three trials, sprigs
of each were placed separately in a plastic chamber, and CO2 change was
measured by a CO2 probe connected to a computer for 5 minutes of full spectrum
light implementation, and 5 minutes of complete darkness (obtained by covering
the chamber with aluminum foil). While the chambers were introduced to light, a
container holding water was kept between the light source and the needle
chamber to minimize temperature increase due to light energy, in an attempt to
eliminate temperature as a variable. CO2 changes were recorded and total rate
of photosynthesis per gram of plant specimen was obtained by subtracting the
CO2 change during darkness (rate of cellular respiration), from the CO2 change
during light implementation (rate of cellular respiration and photosynthesis),
then dividing the figure by the weight in grams of the specimen.

The main variables in this
experiment were light, darkness, duration of light and darkness, CO2
concentration, amount of specimen used, and temperature. Temperature gain was
minimized by the container of water; duration of light and darkness was
measured and controlled; the amount of specimen used was accounted for by
calculating the rate of photosynthesis per gram; and the CO2 concentration was
measured and recorded. No experimental controls were used since this was a
comparison experiment and the only variable which was altered was the color of
the needles, the other variables remained fairly constant.

The results obtained were strange.
The differences between the rates of photosynthesis in the green needles versus
the blue needles were so great that CO2 probe failure is probable. The CO2
change had the tendency to level out, and the results recorded had little
comparative consistency. The P Value obtained from the results further
emphasizes this inconsistency: P = 0.489. In order for the data to be reliable
the P Value must be < 0.05., a huge difference from our P Value. The results
contradict my hypothesis and predictions, demonstrating the direct opposite:
the more negative the rate of photosynthesis (which represents the amount of
CO2 in ppm of each gram of plant specimen per minute), the faster the rate of
photosynthesis. The blue Blue Spruce needles have a much more negative average
rate of photosynthesis (and thus a much faster rate of photosynthesis) compared
to the green Blue Spruce needles. The average rate of photosynthesis of blue
needles is -7.34 (ppm CO2/min/g), compared to -0.420 in green needles. This is
an incredible difference, as demonstrated visually in this graph:

Although the rate of photosynthesis
per gram of plant specimen was obtained, the ratio of needle mass to stalk mass
in each specimen could affect the accuracy of comparison, since the needles
contain most, if not all, of each specimen’s chloroplasts. Another variable
unaccounted for is CO2 concentration in the beginning of each experiment; this
may play a role in photosynthesis rate (perhaps the more CO2 available, the
more CO2 the plant can use in photosynthesis and thus the faster the rate of
photosynthesis). This variable was not consistent at the beginning of each
experiment, and making it so – making the concentration of CO2 in ppm
constant at time 0 for each experiment – could eliminate one source of
doubt. In addition, larger sprigs could be used to increase the CO2 change
during 5 minutes because there would be much more needle mass to conduct
photosynthesis, strengthening the results since the time intervals used were
fairly small. Larger time intervals could also be used to increase the range of
measurement and hopefully the accuracy of results – perhaps light and
darkness periods of 20 minutes each, instead of 5.

Although due to technological
difficulties the data is unreliable and the results are therefore inconclusive,
it would not be unlikely for the results, if the experiment is properly
conducted, to reject my hypothesis. Since the main element of the
photosynthetic reaction center of many photosystems which play a significant
role in the light dependent reactions of many plants is generally chlorophyll a, which commonly has a peak wavelength absorption of
680-700nm depending on the photosystem, this essential part of photosynthesis
may be unaffected by lessened absorption of blue wavelength light (450-500nm).
It is also unclear what wavelengths of light the blue coating actually
reflects, it could be a very small range of wavelengths – this could be
determined by isolating the blue coating and determining its wavelength
absorption and subsequent reflection via a spectrophotometer.

Since one of the main functions of
the accessory pigments in the photosystems, especially in the light-harvesting
complexes, is to mitigate excess energy, the blue reflection may facilitate
this process, making photosynthesis more efficient and thus expediting its
rate. Further experiments to better clarify the results and the implications of
this lab (other than re-conducting the entire experiment to obtain results of
satisfactory accuracy) would be to test the reflection spectrum of the blue
coating, compare the free radical production in blue and green needles to
determine the effectiveness of blue light reflection in reducing free radical
production, and further investigate the effects of different wavelength lights
on photosystem (i.e. light dependent reactions) efficiency.

Depending on the results, real
world applications could also be derived. Perhaps with more knowledge of
nature’s sunscreens, human sunscreens could be better developed to become more
effective in reducing sun damage; roof shingles could be engineered to further
reduce energy absorption and subsequent heat gain in areas of high temperature and
sunlight intensity; contacts could be developed to contain pigments which
reflect damaging light wavelengths and eliminate the need for sunglasses (other
than, of course, to look cool); the applications and extensions could be
endless. Nature is the master of invention and it is time we as a population
reduce our emphasis on improving upon her, and shift our priorities toward
learning from her own research and innovations which have taken billions of
years to conduct.